The invention relates to a thrust dynamic pressure bearing, and more particularly to a thrust dynamic pressure bearing in which negative-pressure suction of a working fluid is prevented from occurring at start of rotation of a sealed thrust dynamic pressure bearing.
As shown in FIGS. 8(A) and 8(B), a thrust dynamic pressure bearing of the conventional art is configured by: a rotor 30 consisting of a shaft 31, and a flange 32 which is disposed on one end of the shaft 31; and a housing 40 which accommodates the shaft 31 and the flange 32 in a hermetically sealed state. In this case, V-like or herringbone-like dynamic pressure generating grooves 33 for generating a radial dynamic pressure are formed in the surface of the shaft 31, or V-like or herringbone-like dynamic pressure generating grooves 34 for generating a thrust dynamic pressure, and the like are formed in end faces 32a and 32b of the flange 32. Small spaces 35 and 36 between the rotor 30 and the housing 40 are filled with a working fluid L for generating a dynamic pressure.
In the thus configured sealed thrust dynamic pressure bearing, at the same time when the rotor 30 is to be started, the dynamic pressure generating grooves 34 of the end faces in the axial direction which are formed in the flange 32 try to suck the working fluid L in a center portion in a radial direction. However, a negative pressure is generated between the upper and lower end faces of the flange 32, because the housing 40 accommodates the flange 32 in a hermetically sealed state, thereby producing a problem in that the working fluid cannot be sufficiently guided into a space between the receiving face of the housing 40 and the lower end face of the flange 32, particularly into a radially inner portion of the space in which the working fluid originally exists in a very small amount. Therefore, small holes 37 are opened in the root portion of the flange 32 (Japanese Patent Publication (Kokai) No. HEI10-196643).
During rotation, the working fluid is simultaneously moved into the V-like or herringbone-like dynamic pressure generating grooves 33 for generating a radial dynamic pressure which are formed in the surface of the shaft 31, and the V-like or herringbone-like dynamic pressure generating grooves 34 for generating a thrust dynamic pressure which are formed in the end faces of the flange 32, and hence a negative pressure is easily generated in the portion where the flange 32 is connected to the shaft 31. In order to prevent the working fluid which is originally small in amount from becoming insufficient, as shown in FIG. 9, a recess 38 is formed in the root portion so as to function as a portion for accumulating the working fluid. Furthermore, a structure has been proposed in which, in place of the recess 38, oblique small holes for circulating a working fluid are formed between the upper or lower end of the flange 32 and the root portion, or radial holes are formed between vertical small holes in the root portion and the end portion of the flange 32 are formed (Japanese Patent Publication (Kokai) No. HEI7-243438).
When the working fluid is insufficient in the spaces between the upper and lower faces (particularly, the lower face) of the flange 32 of the rotor 30 constituting the sealed thrust dynamic pressure bearing and the receiving face of the housing 40 as described above, the bearing cannot function as a thrust dynamic pressure bearing, and may be damaged. In order to prevent such a disadvantage from occurring, it has been proposed to form the small holes 37 for guiding the working fluid to the flange 32 in the vicinity of the shaft as described above. However, this produces problems in that the process of correctly forming the small holes 37 is difficult to perform and increases the production cost, and that a space for forming the small holes is required. Moreover, the bearing area is increased, and hence there arises a problem in that a torque loss is produced. Even when the recess 38 for the working fluid is disposed in the portion where the flange 32 is connected to the shaft 31 as shown in FIG. 9, the working fluid is not sufficiently circulated, so that the tendency to an insufficient amount of the working fluid due to the negative pressure is not solved, thereby producing a problem in that there is a case where negative-pressure suction occurs to cause the thrust dynamic pressure bearing not to function.
The invention has been conducted in order to solve the problems discussed above. It is an object of the invention to provide a thrust dynamic pressure bearing in which complex small holes or the like are not disposed so that the production cost is not increased, and negative-pressure suction which may be caused at start of rotation is prevented from occurring, thereby enabling the bearing to correctly function as a thrust dynamic pressure bearing.
In order to solve the problems, the thrust dynamic pressure bearing of the invention is a thrust dynamic pressure bearing which comprises a rotor (1) and a housing (2) that accommodates the rotor (1) in a hermetically sealed state with forming small gaps (3, 4) therebetween, and in which thrust dynamic pressure generating grooves are formed in one of an end face of the rotor and a face of the housing (2) that is opposed to the end face of the rotor, and the gaps are filled with a working fluid (L) for generating a dynamic pressure, wherein
pockets (1p, 2P) which serve as spaces for accumulating the working fluid are formed in the end face (1a) of the rotor (1) and the end face (2a) of the housing (2) that is opposed to the end face (1a), respectively, and a total of capacities of the pockets (1p, 2P) is 50 times or more a capacity of the bearing gap (3) between the end face of the rotor (1) and the end face of the housing (2).
An embodiment of the invention is characterized in that the bearing gap (3) between the rotor (1) and the housing (2) is inclinedly reduced as moving toward a radially outer side.
Another embodiment of the invention is characterized in that a depth of the thrust dynamic pressure generating grooves (11) is inclinedly larger as moving from a radially inner side toward a radially outer side.
Furthermore, a thrust dynamic pressure bearing of the invention of claim 4 is a thrust dynamic pressure bearing comprising: a rotation shaft (10s) in which radial dynamic pressure generating grooves are formed; and a flange (10f) in which thrust dynamic pressure generating grooves (13) are formed, a recess (16) being formed in a root portion where the flange (10f) is connected to the rotation shaft (10s), a bearing gap (14) between a rotor (10) and a housing (20) being hermetically filled with a working fluid (L), wherein the bearing gap (14) between the flange (10f ) and the housing (20) is formed to be smaller as moving toward a radially outer side.
The above invention may be further characterized in that a depth of the thrust dynamic pressure generating grooves (13) is inclinedly larger as moving from a radially inner side toward the radially outer side.